Hi everyone,
what is the flag for 'pick default value for each config' for portupgrade?

I realize that every now and then when I do a portupgrade my port upgrade stops to the annoying config screens of the ports that it has upgrade and pauses the entire process.

I am interested to know if there's a flag that will take all the default value for all the ports when doing a port upgrade

man portupgrade. You need BATCH=yes option (so called batch mode).
Portupgrade to all ports always a very bad idea!!!. It might work if you system is not too old. It is always far easier to do fresh installation unless you have production machine. If the machine is in production you will normally do portupgrade only if it is necessary for security reasons. You have to read latest portupgrade README to see if there are special instructions for the ports you want to upgrade. Probably yes if it is due for security reasons.

You can use the --batch option with portupgrade if you want the defaults. Or you can use -c or --config if you want portupgrade to run through each of the config dialogs before anything is built. That will allow you to specify options you may want without having the build interupted.